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LEA Advisory 20 Attachment-Inspection Guidance for SW Landfills Page 49 of 52 The lower explosive limit(LEL) of a combustible gas is the lowest concentration of that gas by volume in air that will explode, ignite, or burn when there is an ignition source. For methane, the LEL is 5%. The upper explosive limit(UEL) is the highest concentration of gas that will explode, ignite or burn with an ignition source present. For methane, the UEL is 15%. Below the LEL, there is insufficient fuel to support explosion. Above the UEL, there is insufficient oxygen to support explosion. However, care should be taken as a small dilution with air can bring the level back into an explosive concentration. A violation should be noted if any of the following are found during the inspection: 1. Concentrations of methane exceed 5% or greater by volume in air at the facility property boundary, or 1.25% or greater by volume in air in on-site structures, including underground chambers which are accessible to people; Note: "Facility property boundary" means the boundary designated in the SWFP for the site and does not apply to all the land owned by the operator which may be adjacent to the permitted boundary of the facility. The 5% methane level requirement at the "facility property boundary" does not apply to unpermitted disposal sites. However, §17705 - Gas Control, can be applied at unpermitted sites for methane gas levels above the LEL. 2. A routine methane monitoring program is not implemented with a frequency of monitoring no less than quarterly; 3. The operator has not taken the required measures when methane exceeds the limits specified above; 4. The operator has not complied with the alternative schedule requirement of this standard. An area of concern should be noted if the combustible gas concentration in an on-site structure is between 100 ppm and 12,500 ppm (1.25% or 25% of the LEL). Note: Gas monitoring results and any remediation plans must be placed in the operating record [17258.29(a)(3) - Recordkeeping Requirements]. The inspector should make the above determinations with appropriate instrumentation. Monitoring at the property boundary should be done initially using either a bar hole punch, existing property boundary landfill gas monitoring probes, or a combination of the two. When a gas migration problem is suspected at the site boundary where no landfill gas monitoring probes have been installed and despite readings below 5% by volume in air in bar holes, the LEA should measure methane levels at greater depths. The LEA may request that Board staff use their gas vapor probe equipment to measure combustible gas concentrations to a depth of 20 feet or more, depending on site geology. The LEA should follow up on violations of this section, and require the operator to take adequate steps to monitor and control gas. For purposes of this standard, "at" means as close to the property boundary as possible,but within several feet. The LEA may request Board assistance with technical review of landfill gas control plans. 17258.24 Air Criteria (a) Owners or operators of all MSWLF's must ensure that the units do not violate any applicable http://www.ciwmb.ca.gov/pe/advisoiy/20/attach20/20attch 1.1htm 8/11/98